NWA Unclassified Meteorites

North West African (NWA) Unclassified Meteorites are those found in the deserts of Northwest Africa. Tons of meteorites fall to Earth each year, but they are often hard to find except in areas where they contrast with the surrounding environment, such as a desert or arctic tundra.

The term "Unclassified" means that they have not go through an academic classification process. The ultimate goal of meteorite classification is to group all meteorite specimens that share a common origin on a single, identifiable parent body. This could be a planetasteroidMoon, or other current Solar System object, or one that existed some time in the past (e.g. a shattered asteroid).[citation needed] However, with a few exceptions, this goal is beyond the reach of current science, mostly because there is inadequate information about the nature of most Solar System bodies (especially asteroids and comets) to achieve such a classification.[citation needed] Instead, modern meteorite classification relies on placing specimens into "groups" in which all members share certain key physical, chemicalisotopic, and mineralogical properties consistent with a common origin on a single parent body, even if that body is unidentified. Several meteorite groups classified this way may come from a single, heterogeneous parent body or a single group may contain members that came from a variety of very similar but distinct parent bodies. As such information comes to light, the classification system will most likely evolve.


Ordinary chondrites are the most common meteorites that fall to Earth (~ 74%). Since they tend to have a similar appearance and density as Earth rocks, stony meteorites are difficult to recognize in the field. Unless someone sees them fall, they usually go uncollected. Therefore, although ordinary chondrites are the most common type out in space, they are more rare than iron meteorites in collections on Earth.

Ordinary chondrites show a wide variety of appearances: some light, some dark, some coarse grained, some fine--grained. As their name implies, ordinary chondrites contain chondrules. However, the chondrules in ordinary chondrites are never as distinct as the ones in carbonaceous chondrites. This is a nice indication that ordinary chondrites have been heated to a higher temperature than carbonaceous chondrites, and are therefore less primitive. Almost all ordinary chondrites contain some metallic iron, you can see the iron as bright metallic flakes throughout the sample. Since the rock and iron are well mixed, this implies that the object that the ordinary chondrite came from never differentiated.

Most ordinary chondrites are from the outer parts of an asteroid that suffered destruction by collision. Since ordinary chondrites are the most common meteorite on the Earth, this implies that they represent the most common material in the asteroid belt. Since ordinary chondrites come from bodies that that not been heated very much, this means they come from object that were never very large. This implies that most of the objects in the asteroid belt were never very large.

-- Department of Astronomy University of Washington


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